A large number of wells have been drilled into earth's strata for the extraction of oil, gas, water, and other material there from. In many cases, such wells are found to be initially unproductive, or may decrease in productivity over time. In many of these cases it is believed that the surrounding strata still contains extractable oil, gas, water or other material. Such wells are typically vertically extending holes including a casing used for the transportation of the oil, gas, water or other material upwardly to the earth's surface. In other instances, the wellbore may be uncased at the zone of interest, commonly referred to as an “open hole” completion.
In an attempt to obtain production from unproductive wells and increase production in under producing wells, methods and devices for forming a hole in a well casing, if present, and forming a lateral borehole there from into the surrounding earth strata have been developed and are generally known by those skilled in the art. For example, a hole in cased wells can be produced by punching a hole in casing, abrasively cutting a hole in the casing, or milling out a section of casing. In open hole wells, the steps to form a hole in the casing are not required, but the methods for forming a lateral borehole into the surrounding strata are virtually identical to those used on cased well. Under both the cased and uncased scenarios, a type of whipstock is typically incorporated to direct the nozzle blaster out of the wellbore and into the surrounding formation.
Known methods, however, have generally not been able to provide technically or commercially satisfactory results. For example, when directed at portions of the earth's strata, tests using high pressure fluid exiting a non-rotating fluid nozzle have been incapable of cutting a satisfactory pathway. This shortcoming is due largely to the inability of a stationary type (non-rotating) blaster nozzle to form a passageway into the strata sufficiently large and unobstructed enough to allow for the advancement of the nozzle head. Moreover, the failure of many such systems to adequately address the removal of any formation cuttings that accumulate in the lateral borehole and/or wellbore can impair the efficacy of the jet drilling process. Furthermore, known lateral jetting systems that can effectively cut into formations do not adequately address the centralization of the nozzle head or how to help ensure that it remains on a relatively straight trajectory as it is moved into the earthen strata.
The usage of a rotating nozzle head such as is used in the high-pressure commercial sewer and pipe water cleaning industries, can have applicability to lateral jet drilling, if properly modified. In attempting to directly apply known designs from sewer water blasting to jet drilling, however, one would incur one or more problems. For instance, known rotating nozzle head designs used in commercial sewer and pipe cleaning industries typically employ one or more mechanical bearings and often must incorporate braking or dampening systems to limit their rotational speed. Besides adding undesired complexity, such systems are usually too large (e.g. often 1.25″ to 3″ in diameter) to be easily transitioned around the tight radius of smaller diameter whipstocks, such as those that are used on casing below about 5.5″ in diameter. Besides the difficulty of getting such heads positioned downhole in earthen strata, larger nozzle heads necessitate that more material be removed in order to allow the nozzle to advance. The need to remove more material can dramatically slow down the lateral jetting process, rendering such a method uneconomical on marginal wells. Moreover, the rotating nozzle head on some sewer water blasting or pipe cleaning apparatus extend past the main body, which for purposes of lateral jetting can be highly problematic. For example, the rotating nozzle head can quickly erode if it comes into contact with hard earthen strata; the nozzle head on account of its requisite small size can stop rotating when it comes into contact with the earthen strata because of the minimal torque typically produced by such systems; and, a suitable stand-off distance of the nozzle to the formation is difficult to attain.
The aforementioned issues are further compounded in lateral jet drilling because of the difficulty of precisely controlling the downhole tool string, which is ultimately controlled by an operator who is perhaps many thousands of feet away. For example, a rotating nozzle head as it moves into the earthen strata can stall if unprotected. In addition, the materials released during the lateral jetting process can directly interfere with operation of the nozzle head and/or movement of the flexible hose. Additionally, regardless of whether a rotating, swirling, pulsing or cavitating nozzle is used, such materials can impair the jetting process by filling up the wellbore below the lateral borehole, in turn precluding the removal of cuttings from the lateral borehole.
To control weight on the downhole tools, certain known technologies proscribe utilizing a hose circumscribed with one or more springs. Such a method however is prone to suffer from one or more of the following shortcomings: the springs may provide an opportunity for cuttings or other debris to become trapped therein, bridging off in the lateral borehole, thereby preventing forward movement of the hose; the springs may create turbulent flow patterns allowing for the deposition of cuttings and hence bridging off of the hose; if cuttings become entrapped between one or more coils of the spring, it may cause the nozzle head to change it trajectory or otherwise jam the hose in the lateral borehole; with many formations being naturally fractured, the springs may become stuck in any such cracks or crevices; if the nozzle heads cuts away a softer zone of formation, leaving a ridge or edge, the coils of the spring may become stuck in these; and the coils of the spring may hang-up at the casing due to the occurrence of a incomplete cement-casing bond, potentially causing a catastrophic sticking of the hose in the formation.
Finally, in most known lateral jet drilling methods that can effectively cut earthen formation, the flexible hose used for creating the lateral borehole can become entangled in the tubing sitting atop the whipstock. For purposes of convenience and cost, the production tubing, typically either 2⅜″ or 2⅞″, is commonly used atop the whipstock. Since the typical hose used for lateral jetting is only semi-rigid and commonly of about ½″ to ⅝″ in diameter, the wide spacing between the inside diameter of the tubing atop the whipstock and the outside diameter of the flexible hose can allow the hose to buckle when weight is applied and forward travel of the lower portion of the hose is impeded, such as occurs if the jetting nozzle is not cutting a large enough hole or is cutting at a slower rate than the hose is being moved through the whipstock device.
In view of the above, it would be desirable to have a method and apparatus suitable for horizontal well drilling that can produce a lateral borehole of sufficient size and regularity for advancing the downhole tool string into the formation. It would also be desirable to have a method and apparatus suitable for horizontal well drilling that addresses cuttings that accumulate in the lateral borehole and/or wellbore wherein the creation of such cuttings is problematic. In addition, it would be desirable to have a horizontal drilling method and apparatus that has a small rotating nozzle head that can withstand harsh and varied drilling conditions. In addition, it would desirable to have a means to control the motion of the rotating, swirling, pulsing or cavitating nozzle head so as to keep it on a straight trajectory.